We will study the spatial and temporal dynamics of functional vascular recruitment, neurovascular coupling, and modulation of this response in rodent cortex. We will do this using our established paradigm of high resolution optical intrinsic signal imaging and corroborative electrophysiology. Optical intrinsic signals (activity-related cortical reflectance changes) indicate basic in vivo physiologic processes poorly represented by other indices. A large portion of these signals is thought to arise from vascular dynamics. In support of this, we have used parallel vascular fluorescence imaging (Narayan et al., 1993) to show that optical physiology is related to changes in regional cerebral blood volume (rCBV), and indicates a similar etiology to functional magnetic resonance (fMRI: Belliveau et al., 1991). Paired with electrophysiology, intrinsic signal imaging enables the study of neurovascular coupling, a relationship which is important for understanding brain function as well as for interpreting data from other techniques which incorporate measures of vascular activity at lower resolutions. We will optically map intrinsic signals over rat somatosensory cortex to address three specific aims. First, we will examine the spatial dynamics of functional perfusion. We will determine spatial extent of responses and response location relative to vascular anatomy and electrophysiologic measurements. Second, we will characterize magnitude and timing of the perfusional response. This will include identifying perfusion response threshold as well as identifying dose-response characteristics for the full response curve. Third, we will examine vascular response robustness and modulation in response to competing stimulation. Vascular responses may differ with competing stimuli of varying intensities and temporal patterns. The significance of this proposal is due to the fact that acute activity- related perfusion can be examined with high spatial and temporal resolution. We will assess the development of perfusion redistribution in a variety of stimulation conditions. Issues addressed by this work will assume greater importance as optical methods and fMRI are increasingly applied to the study of brain function.